This invention relates to a mounting structure for a fuel tank on vehicle, such as an automobile that use natural gas and the like as fuels.
Automobiles that use natural gas for fuel (which are hereinafter referred to as "automobiles of the prior art") are equipped with fuel tanks for storing the natural gas in a compressed state. As typically shown in Japanese Patent Unexamined Publication No. Hei. 8-99542, the fuel tank is cylindrical in shape so that the pressure of the contained gas is distributed uniformly in its interior. If one wants to install the cylindrical fuel tank in an automobile, the installation area is limited by its size and shape and a typical example is within a part of the space of the trunk at the rear of the car.
Thus, the installable area of the fuel tank is limited in the automobiles of the prior art. In addition, the fuel tank requires so much installation space that if it is installed in the trunk of the car, the availability of the trunk space is reduced.
The fuel tank must withstand high pressure and the costs of manufacture and quality control increase unavoidably. What is more, the fuel tank must satisfy various regulations on safety and this also contributes to increase the overall cost.
In order to deal with these difficulties, one may think of liquefying natural gas and storing it in the car. To this end, the natural gas has to be held at a cryogenic temperature (say, about -161.degree. C.) within a tank capable of excellent heat insulation (such as one having an evacuated dual-wall structure) and this is another cost increasing factor in the development and manufacture of the fuel tank. As a further problem, a special mechanism such as a vapor chamber for evaporating the liquefied natural gas must be provided and this not only increases the complexity of the system but also requires cumbersome maintenance and management procedures. As a result, the overall cost of the vehicle is increased and at the same time the weight of the car body is increased to cause a significant increase in the cost of servicing the vehicle.